OREGON STATE UNIVERSITY

HJ Andrews Research

Comparing temperature regimes under the canopy in old-growth and plantation forests in the Oregon Cascades, researchers found that the characteristics of old growth reduce maximum spring and summer air temperatures as much as 2.5 degrees Celsius (4.5 degrees Fahrenheit), compared to those recorded in younger second-growth forests.

Landowners who include biodiversity as a management goal, the scientists said, could advance their aims by fostering stands with closed canopies, high biomass and complex understory vegetation.

Management practices that create these types of “microclimates” for birds, amphibians, insects and even large mammals could promote conservation for temperature-sensitive species, the authors wrote, if temperatures rise as a result of global warming.

“Though it is well-known that closed-canopy forests tend to be cooler than open areas, little is known about more subtle temperature differences between mature forest types,” said Sarah Frey, postdoctoral scholar in the OSU College of Forestry and lead author on the study. “We found that the subtle but important gradient in structure from forest plantations to old growth can have a marked effect on temperatures in these forests.”

Temperature is also strongly affected by elevation and even small changes in topography, but the way forests are managed was a critical factor in explaining temperature differences. Researchers at Oregon State and Pacific Northwest Research Station of the U.S. Forest Service conducted the study at the H.J. Andrews Experimental Forest east of Eugene.